/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.handler;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Properties;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.CorsConfigurationSource;
import org.springframework.web.servlet.DispatcherServlet;
import org.springframework.web.servlet.HandlerExecutionChain;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.HandlerMapping;

/**
 * Helper class to get information from the {@code HandlerMapping} that would
 * serve a specific request.
 *
 * <p>Provides the following methods:
 * <ul>
 * <li>{@link #getMatchableHandlerMapping} &mdash; obtain a {@code HandlerMapping}
 * to check request-matching criteria against.
 * <li>{@link #getCorsConfiguration} &mdash; obtain the CORS configuration for the
 * request.
 * </ul>
 *
 * @author Rossen Stoyanchev
 * @since 4.3.1
 */
public class HandlerMappingIntrospector
        implements CorsConfigurationSource, ApplicationContextAware, InitializingBean {

    @Nullable
    private ApplicationContext applicationContext;

    @Nullable
    private List<HandlerMapping> handlerMappings;


    /**
     * Constructor for use with {@link ApplicationContextAware}.
     */
    public HandlerMappingIntrospector() {
    }

    /**
     * Constructor that detects the configured {@code HandlerMapping}s in the
     * given {@code ApplicationContext} or falls back on
     * "DispatcherServlet.properties" like the {@code DispatcherServlet}.
     */
    @Deprecated
    public HandlerMappingIntrospector(ApplicationContext context) {
        this.handlerMappings = initHandlerMappings(context);
    }

    private static List<HandlerMapping> initHandlerMappings(ApplicationContext applicationContext) {
        Map<String, HandlerMapping> beans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
                applicationContext, HandlerMapping.class, true, false);
        if (!beans.isEmpty()) {
            List<HandlerMapping> mappings = new ArrayList<>(beans.values());
            AnnotationAwareOrderComparator.sort(mappings);
            return Collections.unmodifiableList(mappings);
        }
        return Collections.unmodifiableList(initFallback(applicationContext));
    }

    private static List<HandlerMapping> initFallback(ApplicationContext applicationContext) {
        Properties props;
        String path = "DispatcherServlet.properties";
        try {
            Resource resource = new ClassPathResource(path, DispatcherServlet.class);
            props = PropertiesLoaderUtils.loadProperties(resource);
        } catch (IOException ex) {
            throw new IllegalStateException("Could not load '" + path + "': " + ex.getMessage());
        }

        String value = props.getProperty(HandlerMapping.class.getName());
        String[] names = StringUtils.commaDelimitedListToStringArray(value);
        List<HandlerMapping> result = new ArrayList<>(names.length);
        for (String name : names) {
            try {
                Class<?> clazz = ClassUtils.forName(name, DispatcherServlet.class.getClassLoader());
                Object mapping = applicationContext.getAutowireCapableBeanFactory().createBean(clazz);
                result.add((HandlerMapping) mapping);
            } catch (ClassNotFoundException ex) {
                throw new IllegalStateException("Could not find default HandlerMapping [" + name + "]");
            }
        }
        return result;
    }

    /**
     * Return the configured HandlerMapping's.
     */
    public List<HandlerMapping> getHandlerMappings() {
        return (this.handlerMappings != null ? this.handlerMappings : Collections.emptyList());
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @Override
    public void afterPropertiesSet() {
        if (this.handlerMappings == null) {
            Assert.notNull(this.applicationContext, "No ApplicationContext");
            this.handlerMappings = initHandlerMappings(this.applicationContext);
        }
    }

    /**
     * Find the {@link HandlerMapping} that would handle the given request and
     * return it as a {@link MatchableHandlerMapping} that can be used to test
     * request-matching criteria.
     * <p>If the matching HandlerMapping is not an instance of
     * {@link MatchableHandlerMapping}, an IllegalStateException is raised.
     *
     * @param request the current request
     * @return the resolved matcher, or {@code null}
     * @throws Exception if any of the HandlerMapping's raise an exception
     */
    @Nullable
    public MatchableHandlerMapping getMatchableHandlerMapping(HttpServletRequest request) throws Exception {
        Assert.notNull(this.handlerMappings, "Handler mappings not initialized");
        HttpServletRequest wrapper = new RequestAttributeChangeIgnoringWrapper(request);
        for (HandlerMapping handlerMapping : this.handlerMappings) {
            Object handler = handlerMapping.getHandler(wrapper);
            if (handler == null) {
                continue;
            }
            if (handlerMapping instanceof MatchableHandlerMapping) {
                return ((MatchableHandlerMapping) handlerMapping);
            }
            throw new IllegalStateException("HandlerMapping is not a MatchableHandlerMapping");
        }
        return null;
    }

    @Override
    @Nullable
    public CorsConfiguration getCorsConfiguration(HttpServletRequest request) {
        Assert.notNull(this.handlerMappings, "Handler mappings not initialized");
        HttpServletRequest wrapper = new RequestAttributeChangeIgnoringWrapper(request);
        for (HandlerMapping handlerMapping : this.handlerMappings) {
            HandlerExecutionChain handler = null;
            try {
                handler = handlerMapping.getHandler(wrapper);
            } catch (Exception ex) {
                // Ignore
            }
            if (handler == null) {
                continue;
            }
            if (handler.getInterceptors() != null) {
                for (HandlerInterceptor interceptor : handler.getInterceptors()) {
                    if (interceptor instanceof CorsConfigurationSource) {
                        return ((CorsConfigurationSource) interceptor).getCorsConfiguration(wrapper);
                    }
                }
            }
            if (handler.getHandler() instanceof CorsConfigurationSource) {
                return ((CorsConfigurationSource) handler.getHandler()).getCorsConfiguration(wrapper);
            }
        }
        return null;
    }

    /**
     * Request wrapper that ignores request attribute changes.
     */
    private static class RequestAttributeChangeIgnoringWrapper extends HttpServletRequestWrapper {

        public RequestAttributeChangeIgnoringWrapper(HttpServletRequest request) {
            super(request);
        }

        @Override
        public void setAttribute(String name, Object value) {
            // Ignore attribute change...
        }
    }

}
